Reflector



Feb. 11, 1930. w, UTTLE 1,746,399

REFLECTOR Filed Dec. 1.1925 2 SheecS-Sheet 1 INVENTOR xii/Z4,

0 BY a/z zw 3 ATTORNEY Feb 11-, 1930.

w. F. LITTLE 1,746,399

REFLECTOR Filed Dec. 1. 1925 2 sheets-sheet 2 l NVENTOR QBY PatentedFeb. 11, 1930 v UNITED STATES WILLIAM E. LITTLE, OF NEPPERHAN HEIGHTS,NEW YORK REFLECTOR Application filed December My invention relates toreflectors for incandescent lights and is particularly adapted for usein automobile headlights railroad signals, flash lights, or the'like. Anobject of my invention is to provide a reflector giving suflicientvertical spread to properly illuminate the roadway without producingundue glare in the eyes of an approaching motorist, and to produce abeam of relatively Wide spread having a nearly uniform crosssection,such as is desirable for signal and flash light beams.

Another object is to provide a reflector of such character as toaccommodate itself to commercial variations in incandescent lamp bulbs,Without requiring refocusing and without substantial variation in theilluminating properties of the resultant beam. In other Words, I producea set-focus reflector.

A further object is to provide a reflector of such character that evenwith the light source located slightly on either side of the focalpoint, the nature and spread of the field of light will be maintainedsubstantially uniform.

A further object is tominimize the upward rays of light so as to reduceglare.

Experience has shown that the beam projected from the parabolicreflectors in common use (1% inch focal length) with standard types ofautomobile headlight, are of insufficient vertical spread to properlyilluminate the roadway. It is therefore customary to make use ofadditional means for increasing the vertical spread.

The parabolic reflector projects a beam approximately 2 vertically by 3horizontally (the elliptical shape being due to the construction of thefilament). If this beam is merely widened horizontally, a narrow band oflight is projected across the roadway, leaving the nearby and extremedistance (150 feet and beyond) in darkness.

vIn addition to the objection of projecting a narrow beam, the parabolicreflector is extremely sensitive to focal adjustment because the centerof each cone of light projected by any part of the. reflector falls inthe center of the beam, and the cones superimpose, and

therefore all cones overlap, those from the 1, 1925. Serial No. 72,475.

center of the reflector being of greater angular spread than those fromthe edges. The slightest movement of the light source will cause thecone axes to cross or diverge and produce a dark center in the beam.

To remedy the defects referred to in the parabolic reflector and providea reflector projecting a beam of suificient vertical spread and lesssensitive to focal adjustment, my reflector has been designed in such away that each element of the reflector will project a fan shoped beamsubtending the desired angle of spread, rather than each infinitesimalarea of the reflector projecting the beams with parallel axes. I

In orderthat m invention may be better understood, attention is directedto the accompanying drawings in which:

Figure 1 is a vertical side sectional view of my improved reflector withan incandescent light and socket located therein in the usual manner, i.e., arranged so as to be coincident with the reflector axis;

Figure 2 is a vertical front view of the same reflector showing it to besymmetrical and with the lamp axially arranged and also showing thelocation of the name or trade mark or other printing for the purpose ofdulling the reflector surface to reduce the upward rays of light fromthis portion;

Fig. 3 is a vertical sectional view of my improved reflector and is amodification of Fig. 1 showing the preferred location and position ofthe incandescent lamp;

Fig. 4: is a plan view of Fig. 3 showing the preferred arrangementemploying vertical or nearly vertical flattened sections;

Fig. 5 is a vertical sectional view of my reflector showing thecharacteristics of various portions ofthe reflector surface; and

Figure 6 is a vertical sectional view illustrating the principleunderlying the construction of my improved reflector, said principlebeing applied to my reflector in which for purposes of illustration, thegenerating element is in the form of a hyperbola.

To meet the requirements of the best type of headlamp, the beam must beuniformly bright, or nearly uniformly bright throughout its diameter andits limits must be well defined. Furthermore, the beam should have aspread of at least in order to cover a sufficient area along the road.

To allow for manufacturing inaccuracies, fila'ment distortions and thelike, every art of the beam pattern must receive light rom more than onesection of the reflector. Therefore, there must be superimposition oflight cones from op osite sections of the reflector.

In my re ector the opposite elements project beams that superimpose,thereby causing suflicient overlapping to eliminate filament ima es andother irregularities of like nature. bus, in Fig. 5 the rays reflectedfor example from point A superimpose over the rays reflected from pointB, while the rays reflected from points C and D also superimpose. Thisholds good for corresponding points in the element on one side of t eaxis which superimposes with the corresponding points in the element onthe opposite side of the axis. 1

The construction of my reflector is such that the most sensitive part tofocal adjustment (namely, that between and 75 to the reflector axismeasured from the reflector vertex, or that zone of the reflectoraproximately embraced within the brackets F. and E) reflects lights tothe center of the beam, whereas the rest of the reflector surfaceprojects light to the outer edge of the beam.

With this construction approximately half of the rays projected fromeach element from the center half way out) cross the reector axis. Theremaining rays (from half way out to the edgeg are divergent thereto.Thus, for the same ocal length the crossing over of the beams fromopposite elements permits of a deeper reflector, of if the reflector isnot deeper, the arrangement permits a greater focal length.

' It will be seen, therefore, that a reflector of this design can bemade to cover any desired angle of spread, and that for the samediameter and same focal length will have a greater depth and subtend agreater solid angle of light flux. 1

s the reflector can be made to produce any desired spread, and asexperience has shown that a spread of 5 is desirable, each element ofthe reflector is designed to project beams to cover 3, the physical sizeof the filament (providing the two additional degrees of sprea As thegreater the focal length of any reflector the less its sensitiveness tofocal adjustment, my reflector may be provided with a greater focallength, at the same time subtending the same solid angle of light fluxas the standard parabolic reflector. I proose making a reflectorutilizing a focal ength of one and one-half inch, instead of thestandard parabolic focal length of one and one-quarter inch.

The portion of the reflector most sensitive to focal adjustment (or thatzone of the reflector approximately embraced within the brackets E, E)with the light source at the focus, projects light to the center of thebeam, as a result of which, any change in the position of the lightsource will produce the minimum change in the beam diameter.

It will be noted that as opposite elements project beams whichsuperimpose, the only portions of the reflector which project light inan upward direction (assuming the light source is approximately at thefocus) will be the top thereof, i. e., that portion approximatelyembraced within the bracket H, and a narrow semicircular band near thecenter of the reflector immediately below the axis, i. e., that portionapproximately embraced within the bracket 1. Therefore, by covering theupper portion H of the reflector so as to dull its reflecting propertiesby a name, trademark, or the like as at 0, Fig. 2, or deflectin it witha prism and bringing the socket hol ing the bulb in an upward directionfrom below the reflector vertex at an angle of 15 to to the reflectoraxis, thus eliminating the reflection from the band, as at P, Fig. 3, atthe same time properly positioning the filament at the focus of thereflector, a beam of flattened top will be projected with substantiallyno loss of light. Also this construction produces the point of maximumintensity near the top of the beam where it is most useful.

With the lamp filament tilted as in Fig. 3, the greatest area offilament will be presented toward the upper portion of the reflectorbetween the angles of 0 and to the reflector axis, or that portionapproximately embraced within the bracket J, and the lower portion ofthe reflector between 60 and 105 to the reflector axis, or that portionapproximately embraced within the bracket K. Conversely, less filamentarea will be presented toward the upper portion of the reflector between60 and- 105 to the reflector axis, or that portion embraced within thebracket L and the lower portion of the reflector between 0 and 60 to thereflector axis or embraced within the bracket M. Therefore, the portionof the reflector which throws a downward light projects beams of widerspread than the portion which throws upward light, because'the broaderprojection of the filament is presented to the portions of the reflectorwhich project the downward rays of light. For this reason the completebeam will have less light above the point of maximum intensity thanbelow it. Consequently the reflector is less sensitive to focaladjustment than the parabolic reflector, that is, the lamp filament maybe moved a relatively great distance from the focal point of myreflector without projecting light in an upward direction. The upwardlight produces the glare under service conditions.

approximately uniform brightness In positioning the filament, if themajor portion of it is moved slightly below the focal point, a slightlyelongated beam cross-sect on will be pro'ected with the brighter portionnear the re ector axis, or near the top of the beam, and ta ering offtoward the bottom of the beam. I this beam be widened horizontally witha vertically fluted or corru ated front glass, a deep beam approximate y5 or 6 high, and any width desired, may be projected. By tilting thereflector axlsdownward this beam will have a olnt of h gh intensity nearthe horizontal or long distance light, tapering olf to illuminate nearbyand less important points in front and to the side, thus providing anilluminated roadwa of rom points near the car to distant points.

To illustrate the principles of my invention as applied to a reflectingsurface, Figure 6 is shown as an example, in which the generatingelement is a hyperbola, although it 1s readily understood that the samepr nciples could apply just as well if the generating element were aparabola and ellipse or a combination of these forms. To secure areflector having the above outlined advantages, a curve has beendeveloped, such that if a narrow strip of reflecting material (areflector element) be constructed to this curve, and an 1ncandescentfilament placed at or near the focal point, the rays of light from thereflector would travel in a fan-shaped beam havinga divergence of 5 fromthe reflector ax1s. If the beam pattern is to be uniformly bright andmade up of superimposed cones, then the most efficient means ofobtaining such superimposition is to construct a symmetrical reflector,opposite elements of which are made to project the same types offan-shaped beams completely overlapping.

A curved strip as above referred to, can be laid out in the form of anelement of a hyperbola. The revolution of hyperbola around its true axiswould result in a regular hyperbloid and no superimposition of lightbeams,

would occur. The above desirable superimposition of light beams may besecured by selecting an axis not coincident with the true axis of thereflector and around which the hyperbolic element may be rotated has ageneratrix to form this improved reflector surface. Thus, if thehyperbolic element be rotated about an axis Z-Z Figure 6, throu h thefocal point p and drawn parallel to t e bisector Pp of the fan-shapedbeam, then" the reflector will be a surface of revolution (not ahyperbloid because the axis of revolution Z--Z was not coincident withthe true axis po of the hyperbolic element A-0) op posite elements ofwhich will project fanshaped beams completely overlapping.

It will be evident that a reflector of this character will be leastsensitive to the movement of 'the filaments away from the focal pointbecausestarting with the filaments at the focal point and moving it inany direction it can move a maximum distance (because of the overlappingof the beams) without producin a beam of dark center and by thus closing1n the hyperbolic elements and crossing the fan-shaped beams, a longerfocal length reflector can be used for a given collecting angle and thegreater the focal length the less the sensitivity.

Thus in Figure 6, a regular hyperbolic reflector, such as A OB, with thelight source located at the focal point p, would reflect divergent beamsof light as though the light source were located at the conjugate focuspoint 12 However, in my improved reflector, a symmetrical reflectingsurface A()--B, is produced by rotating the hyperbolic elements A'Oabout the selected axis Z--Z parallel to the line P-p which bisects thelight beam from the hyperbolic element AO. Thus, the fan-shaped lightbeams from the hyperbolic elements AO and OB' superimpose and result inmy improved light. It will be noted that in an ordinary hyperbolicreflector, the conjugate focus is a single point p while in my improvedreflector, the conjugate foci fall in a series of points 17, pdescribing a circle.

The inclusion of vertically or nearly vertically flattened sections tospread the beam laterally, as shown in Fig. 4, will not in any wayaffect the insensitiveness of my improved reflector to focal adjustmentor in other words its set-focus characteristic. These flattenedsections, if provided, will project overlapping flattened beams, and thereflector will project the desired beam pattern without the aid of amodifying lens.

Having now described my invention, what I claim as new tl18IBl11' anddesire to secure by Letters Patent is as follows:

1. An improved reflecting surface formed by the revolution of ahyperbolic element around an axis, said axis passing through the focalpoint and parallel to a bisector of the fan-shaped beam projected fromsaid hyperbolic element, thus making the opposite fanshaped beamsoverlap and form a round uniforml bright beam.

2. improved reflector of which each element is hyperbolic and projectsfrom center to extremity, a diverging beam equal to the extreme width ofthe reflector beam pattern, said element being rotated about an axispassing through the focus and making an angle with the hyperbola axis sothat beams from said elements located diametrically opposite withrespect to said axis of rotation, completely overlap and eliminatestreaks from manufacturing irregularities and filament images.

tersects the true hyperbolic axis at an angle, the opposite hy erbolicelements project overlappin fan-s a ed beams of any desired spread, anan incan escent lamp placed with 5 its axis at an angle to the reflectoraxis, the base downward, so that the projected area of the filament isgreatest toward that part of the reflector which pro'ects downwardlight, and the least projecte area of the filament 19 toward that partof the reflector which pro- 'ects upward light, and locating the lampase in such a position that it intersects the light rays whic wouldotherwise be projected upwardly at the greatest angle to the 5 reflectoraxis.

4. An im roved reflector which is a surface of revo ution formed by therotation of a hyperbolic element about an axis passing through the focusand parallel to a median 2n line bisecting the normal fan-shaped beamprojected from said by rbolic element so that the rays of li ht flibmsaid reflecting surface are able to c iange their direction the maximumamount without forming a dark centered beam pattern for a. givendisplace ment of the light source along the axis from y the focal point.

This specification signed this twenty fifth day of November, 1925. v :0WILLIAM F. LITTLE. x

